A study of the steroid metabolic activity of estrogen receptor positive and estrogen receptor negative human breast cancer as well as a correlation between the steroid metabolic activity and the clinical response to endocrine ablation and hormone therapy in female patients with advanced breast cancer is currently under investigation. Estrogen receptor content using the sucrose gradient and dextran coated charcoal methods will be determined on tumor tissues. The metabolism of pregnenolone, dehydroepiandrosterone, 16-hydroxydehydroepiandrosterone, estradiol and estrone will be carried out using the same tissues for which estrogen receptor content was determined. Follow up of patients undergoing treatment using endocrine ablation or hormone therapy and response to therapy will be determined according to criteria used by the Medical Oncology group at the University of Minnesota.